Mutant of Geotrichum candidum which produces novel enzyme system to selectively hydrolyze triglycerides

ABSTRACT

A mutant fungal strain, namely G. candidum NRRL Y-552, mutant known as Henkel 9-2-3-9 (ATCC 74170) produces a lipase called &#34;UNLipase&#34; providing a selectivity of 25:1 for oleic acid over palmitic acid by the assay procedure employed. UNLipase has a temperature range of operation of between 0 and 40 degrees Celsius (and no activity over 55 degrees Celsius). The optimum pH ranges are between 7.5 and 8.5. Magnesium cations increase activity, whereas calcium cations are inhibitory. The molecular weight of the protein appears to be 65 kDa by size exclusion chromatography. UNLipase shows a high degree of selectivity for hydrolysis, esterification and transesterification.

FIELD OF THE INVENTION

The present invention relates to a novel mutant strain of Geotrichumcandidum and a novel lipase produced by that strain, UNLipase whichselectively hydrolyzes oleic acid esters at superior rates over othersaturated and unsaturated fatty acid esters, such as palmitoleic, andstearic esters.

BACKGROUND OF THE INVENTION

Glyceride cleavage is typically performed in industry usinghigh-temperature steam treatment which does not discriminate betweensaturated and unsaturated fatty acid or fatty acid chain length. The useof enzymes, particularly lipases, as catalysts for efficient glyceridesplitting at mild, low energy-demanding conditions would offer manyeconomic advantages over these prior methods. The use of a selectivelipase for the preparation of high purity oleic acid from fats or oilscontaining low levels of oleic acid would offer additional economicadvantages over these prior methods.

A. Lipases, Generally

Lipases are a group of enzymes belonging to the esterases, and are alsocalled glyceroester hydrolases or acylglycerolacylhydrolases. Theseenzymes hydrolyze fat and oils (present in ester form, such asglycerides), yielding the base components of glycerol and fatty acids.These enzymes also catalyze digestion. Lipases are widely foundthroughout the plant and animal worlds, including molds, bacteria, milkand milk products, and animal tissues such as the pancreas. Lipases havebeen widely used to split fats without damaging sensitive constituents,such as vitamins or unsaturated fatty acids. (The Merck Index, p. 868).

Lipases generally have two types of specificity, positional specificityand fatty acid specificity. Positional specificity or regiospecificitypermits some lipases to split the ester bonds at particular positions onthe triglyceride backbone. Aspergillus niger lipases display this typeof specificity. Hata et al., J. Biochem. 86:6, 1821-1827 (1986).Pancreatic lipase and Pseudomonas fragi lipase reportedly attacktriglycerides at the 1-, 3-positions. Alford et al., JAOCS 42, 1038-40(1961). An ideal lipase for total fat splitting would have the followingproperties: 1) broad substrate specificities, 2) no significantinterferences, 3) high specific activity, 4) a degree of hydrolysis of100%.

Fatty acid specificity is displayed by lipases which indiscriminatelysplit all of the ester bonds. Certain amounts of fatty acid specificityhave been found in some Geotrichum candidum lipases. Hata et al., J.Biochem. 86:6 1821-1827 (1986). These lipases are generally specific forcertain chain length fatty acids or double bond positions. Osterberg etal., JAOCS, 66:9 (1989).

B. Prior Research on Geotrichum Candidum Lipases

G. candidum is a mold with septate mycelia, found growing on sour creamand cheese in a firm white mass. Jensen, Lipids, 9, 149-157 (1974). Ithas long been known for its relatively selective lipases. Whileextensive research has been performed on G. candidum lipases, littlesuccess has been achieved with regard to obtaining a truly selectivelipase.

A close examination of the prior art indicates that, while it has beenknown that G. candidum lipase has selectivity for oleic acid containingtriglycerides over short chain fatty acids and saturated fatty acids, nolipase has attained the level of oleic acid selectivity shown by theUNLipase, which means Unsaturation-specific Lipase, enzyme of thepresent invention. Please see the following discussion of the prior art.

DESCRIPTION OF THE PRIOR ART

The following is a brief description of G. candidum lipases culled fromthe scientific references as indicated.

Wilcox, J. C., Nelson, W. O. and Wood, W. A. J. Dairy Sci. 38:775(1955). Jensen (1973) reports that this article contains the first hintthat Geotrichum Candidum lipase is specific for cis-9-unsaturation sincethe lipase hydrolyzed olive oil but not butterfat. Jensen notes that theability to characterize different free fatty acids was limited in 1955,so that the researchers could not analyze their results to see thatmostly oleic acid had been freed from the oils.

Alford and Pierce, "Lipolytic Activity of Microorganisms at Low andIntermediate Temperature. III. Activity of Microbial Lipases atTemperatures below 0° C." J. Food Sci. 26:518-524 (1961). Alford reportsthe first studies on the specificity of G. Candidum lipase forunsaturated fatty acids in natural oils. Alford et al. demonstrates alsothat the specificity is increased at lower temperatures. Alfordhypothesizes that this is due to the changing physical structure of thefat. The lipase hydrolyzed 73% of the substrate triglycerides into freeoleic acid.

Alford and Smith, "Production of Microbial Lipases for the Study ofTriglyceride Structure", JAOCS 42:1038-40 (1961) Reports a selectivelipase from G. candidum. Alford and Smith suggest that G. Candidumlipases attack primarily unsaturated fatty acid linkages. However,subsequent reports have contradicted this observation, see Franzke etal. below.

Alford, J., Pierce, D. and F. Suggs, J. Lipid Res 5:390 (1964). Thispaper confirmed the specificity of G. candidum lipase for oleic acidwith synthetic triglycerides as substrates. The level of specificity isfar lower than that disclosed by the Henkel mutant strain.

Alford, J. and J. Smith, JAOCS, 52:1038 (1965). This article discussedimproved production of G. Candidum through particular media, and did notexplore the selectivity of the lipase for saturated and unsaturatedfatty acids.

Franzke et al., Zentralblatt Fuer Pharmakotherapie UndLaboratoriumsdiagnostik, 111:1025-1033 (1972) described a selectivelipase for G. candidum however, hydrolysis of butterfat resulted in therelease of 24% palmitic acid as well. Also, the hydrolysis of palm oilreleased more than 70% saturated fat. See also, Kroll, J., Franzke, C.,and Genz, S. Pharmazie 28:263 (1973) (isolation of a lipase with a M.W.of 32 kDA).

Iwai et al., "Lipid Requirement for the Lipase Production by Geotrichumcandidum Link", Agri Biol Chem. 37:4,929-931 (1973) The authors reportthe separation of lipase by 44-fold with an estimated molecular weightof 53-55,000 daltons. The lipase is characterized by requiring thepresence of lipid (lipid induction) in the medium for production of theenzyme. The study focuses on the production of lipase, not the reactionsit undergoes nor its selectivity.

Jensen, R. G., "Symposium Microbial Lipolytic Enzymes", Lipid (1974).This paper characterizes the positional and fatty acid specificity of alipase isolated from Geotrichum. The particular strain of Geotrichum hasbeen lost preventing the work from being repeated.

Kroll et al., "Preparation and Properties of the Immobilized Lipase forGeotrichum candidum" Die Nahrung, 24:215-225 (1980). Lipase for G.candidum (strain unknown) was isolated and immobilized on cellulosecolumns. Enzyme activity of 58-66% was reported, and fatty acidspecificity remained unchanged.

Kimura et al., J. Appl. Microbiol. Biotechnol. 17:107 (1983).

Japanese Patent 59-93,889, "Method for Producing Oleic Acid", (1984).This patent deals with the general area of enzymatic hydrolysis oftriglycerides with any of a number of enzymes coming from the"Diotrichum" microbe, which is assumed to be "Geotrichum". This patentdeals more with the separation of the liberated acids than theselectivity and activity of the enzyme itself.

Ishida et al., "Oleic acid production for oils and fats", Jpn. KokaiTokyo Koho, JP 60,237,997 (filed May, 1984). Edible oils and fats arereportedly hydrolyzed with Diotrichum candida lipid hydrolyzing enzymeat a rate of over 70%. The unhydrolyzed portion is then fractionatedusing steam and oil-water phase separation to produce oleic acid. Thisabstract highlights the difficulty of obtaining highly purifiedquantities of oleic acid, even in normal enzymatic systems. Ishida etal. was forced to resort to non-enzymatic separation techniques toachieve sufficient purity.

Hata et al., "Low Resolution Crystal Structure of Lipase from Geotrichumcandidum (ATCC34614), " J. Biochem. 86:6, 1821-27 (1986) This study onlydiscusses the structure of lipase from a different strain of G.candidum.

Tahoun, Fat Sci. Tech. (1987). Results demonstrated in this articlereport on a 2 fold increase in hydrolysis of triolein over thetripalmitin in a G. candidum lipase preparation. Also, the "mycelial"lipase isolated by Tahoun is different from the lipase of thisinvention. This conclusion is further supported by the high molecularweight of the Tahoun enzyme, namely 79 kDA (specific activity of 327).

Vandamme et al. "Cloning of the lipase gene of Geotrichum candidum inEscherichia coli and yeast", EP 243 338 (filed, Apr. 25, 1986). Thisabstract discusses mainly the cloning of a gene coding for G. candidumextracellular lipase. The abstract notes that such lipase "displays aunique specificity for fatty acids which have a cis-9 double bond" butdoes not give the source of this information. The abstract does notindicate which lipase has been sequenced as well.

EP 87-870055.8, "DNA sequence coding for specific lipase vectors for theexpression thereof, microorganisms transformed by these vectors and useof these microorganisms for the production of the lipase", Labofina thepatentee, describes a sequence which would give rise to a protein with amolecular weight of about 29 kDA and perhaps demonstrates the low"selectivity" which has been known for years. Although the patent hasbroad claims, there is very little support for the selectivity describedtherein.

PCT/US88/03480. Lubrizol Corp. describes the use of enzymes to hydrolyzesunflower oil and the separation of the high oleic acid product.According to this reported abstract, 88% to 94% hydrolysis using U.S.rugosa lipase (not G. candidum) was utilized against sunflower seed oil.Sunflower seed oil is an oil with high concentrations of oleic acidpresent in the triglycerides.

Piazza et al., "Lipolysis of Olive Oil and Tallow in an Emulsifier-FreeTwo-Phase System By the Lipase from Oat Seeds", Biotech. Letters, 11:7,487-492 (1989). This paper describes the specificity of seed lipases formonounsaturated fatty acids.

Lazar, G. and Eirich, L. D., "Hydrolysis of tallow, olive oil andcoconut oil by extracellular, intracellular and membrane-bound microbiallipases-lipase-catalyzed lipid hydrolysis (conference abstract), Biol.Chem. Hoppe Seyler (1989), 370, 9, 985 (Henkel).

"The substrate specificity of extracellular, intracellular andmembrane-bound lipase (EC-3.1.1.3)-containing fractions of . . .Geotrichum candidum was determined using tallow, olive oil and coconutoil as substrates. After limited enzymatic hydrolysis of thetriglycerides, the proportion of fatty acids were determined andcompared to the total chemical hydrolysis . . . [A]11 lipases from G.candidum showed a very strong specificity for oleic and linoleic acids.Thus, different lipase fractions from a particular microorganism canhave very different substrate specificities and, to a certain extent,substrate specificities are dependent upon the triglyceride hydrolyzed."

Jacobsen et al., Enzyme Microb. Technol. (1989) 11,90-95. This papercharacterizes several enzymes from a general strain G. candidum. Oilinduction of enzyme production by G. candidum was utilized to preparethe enzyme, distinguishing from Henkel's innovative enzyme production.Finally, the article is solely related to "extracellular" lipase andfails to examine selectivity between palmitic and oleic acid.

Baillargeon et al., "Evaluation of strains of Geotrichum candidum forlipase activity and fatty acid specificity", App. Microbiol. Biotech.,30, 92-96 (1989). This article examines three Geotrichum candidumstrains, namely ATCC34614, NRRL Y-552 and NRRL Y-553. Using two crudelyprepared commercial lipases as controls, the researchers did not observeany discrimination of the lipases from the strain utilized by Henkel,NRRL Y-522 or ATCC 34614. The researchers did observe preferentialspecificity for hydrolysis in NRRL Y-553.

The researcher utilized enzymatic reaction rates for pure oleic andpalmitic acids, then comparing the ratios of the specificity constants.The rates of Y-553 were significantly higher than those prepared fromY-552, which only preferred oleic acid over palmitic acid at a ratio of1.5 or not at all. This reference teaches away from the highly positiveresults of the mutant obtained from Y-552 by researchers at Henkel.Baillargeon states that the "specificity of the G. candidum lipasesapparently varies greatly with strain." Baillargeon also states thatrelative rate ratios in the range of 10-15:1 would be "industriallyuseful for the separation of unsaturated fatty acids."

Hills, "Enzymatic Fractionation of Evening Primrose Oil by Rape Lipase:Enrichment of Gamma-Linolenic Acid", Biotechnology Letters, 2:9, 629-632(1989). Rape lipase catalyses the production of esterification of oleicacid with butanol 35 times faster than GLA (Gamma-Linolenic Acid).

Jacobsen et al., Biotechnology Letters 12, 121-126 (1990) produced ahydrolytic rate for the methyl esters of oleic acid 10 times better thanthe rates for palmitic methyl ester. However, no rates for natural orsynthetic triglycerides were reported.

U.S. Pat. Nos. 4,719,178 and 4,861,716 describe the use of G. candidumas for the hydrolysis of esters of a particular type of long chain fattyacid; U.S. Pat. No. 4,683,987 describes the use of lipase from G.candidum in the esterification of 2-halopropionic acid. U.S. Pat. No.4,275,081 teaches the use of G. candidum in the randomization of fattyacid radicals in the glyceride position and U.S. Pat. No. 4,275,011utilized G. candidum in the production of glyceride.

SUMMARY OF THE INVENTION

The present invention relates to a novel strain of Geotrichum candidumATCC No. 74170 as well as novel enzyme UNLipase, an extracellular oleicacid-selective lipase produced by this organism. This invention alsoincludes within its scope a novel process for the production of themutant strain.

The process for the production for this novel strain comprises

a.) culturing Geotrichum candidum NRRL Y552 in a nutrient medium, e.g.nutrient agar;

b.) exposing the cultured strain to ultraviolet light for a sufficientperiod of time to induce mutation;

c.) incubating the resulting mutants with agitation in a nutrient broth;

d.) freezing the suspension;

e.) thawing the suspension and

f.) repeating steps a.) through e.), yielding the desired organism.

The nutrient broth comprises a mixture of about 1% to about 10% byweight of partially hydrolyzed proteins suitably from animal orvegetable origin (peptones), e.g. trypticase peptone, bactopeptone, soypeptone, casamino acids, NZ-amine® or casein in water. A 5% trypticasepeptone in water is the nutrient broth typically employed.

The UNLipase according to the present invention is particularly usefulin obtaining high purity oleic acid from fats and oils with theadvantages of a) requiring low temperatures (23°-45° C.) and b)requiring neutral pH (6.0-8.0) yielding a product stream of oleic andlinoleic acids with saturated mono-, di- and triglycerides. Furthermore,the catalyst can be immobilized rendering it suitable for cycling ineither a batch or continuous mode of operation. The oleic acid selectivelipase can be used for the selective esterification of oleic acid andother unsaturated fatty acids from mixtures of saturated and unsaturatedfatty acids. UNLipase can also be used for the selectivetransesterfication of esters of oleic acid from mixtures of saturatedand unsaturated esters.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a strain of Geotrichum candidumidentified by ATCC deposit no. 74170 and the corresponding mutants andvariants of this-strain as well as a novel lipase produced by the straincharacterized by an increased selectivity for unsaturated fatty acidhydrolysis from triglycerides and other esters. The strain identified asGeotrichum candidum ATCC 74170 was deposited with the American TypeCulture Collection, 12301 Parklawn Drive, Rockville MD 20852-1776, onJul. 8, 1992. Included within the scope of this invention is amutagenesis and selection process for the production of this strain.This invention also includes the process of selective hydrolysis ofoleic and other unsaturated fatty acids from fats and oils utilizingthis lipase of the invention.

The lipase product according to the present invention is identified asUNLipase.

The process for the production of the G. candidum mutant is as follows.

Source of G. candidum strain: G. candidum strains were obtained from theUSDA culture collection in Peoria, Ill. In particular, the strain NRRLY-552 (ATCC#74169) was chosen.

Culture media: Typically, the mutant strain of Geotrichum candidum NRRLY-552 is prepared by culturing the strain in culture plates for 3 or 4days in nutrient agar, rinsing off the culture plates with sterile waterto obtain single-cell arthrospores, exposing the culture plates toultraviolet light for a predetermined period of time to produce mutants,placing the mutants in a broth composed of 5% bactopeptone, shaking ateight degrees Celsius for twenty-four hours to create a suspension,freezing the suspension at-5 degrees Celsius, thawing the suspension,culturing mutants from the suspension, and repeating the process.

The novel mutant which is known by Henkel's internal number 9-2-3-9 asstated above is identified by the ATCC deposit no. 74170.

The desired UNLipase is hanFested from the cultured cells as follows

1. Enzyme Preparation

The Enzyme was harvested using centrifugation at 5000 rpms, for example,in a Beckman GSA rotor for 10 minutes. This cell-free preparation wasused to determine hydrolysis, esterification and transesterificationproperties.

2. Substrate Preparation

Substrates were prepared in isooctane (2,2,4-trimethylpentane) at about0.8 grams per 20 ml solvent. Assay procedures for determining lipaseactivity were those described by Kwon, D. Y. and Rhee, J. S., J. Amer.Oil Chem Soc. 63:89-92(1986). One modification was to perform someassays for one hour under nonagitated conditions to avoid difficultiesin reproducing agitation rates.

The UNLipase has a molecular weight in the range of about 35,000 to70,000 Daltons has a pH range of 5.0 to 9.5 with an optimal pH range of7.5 to 8.5 and a temperature range of 0° to 40° C. with a T_(max) =32°C. It is inhibited by calcium ions at 25 mM concentration but activatedby magnesium ions at concentration of 25 mM.

Selectivity of UNLipase

1. Hydrolysis of pure triglycerides with UNLipase

Pure triglycerides of caprylic (C8), caproic (C10), lauric (C12),myristic (C14), palmitic (C16), stearic (C18), arachidonic (C20),palmitoleic (C16:1), oleic (C18:1) and linoleic (C18:2) were prepared asdescribed under "substrate preparation" and reacted with UNLipase in thepresence of water for 1 hour at 37 degrees C. Hydrolysis was greatestfor triolein, with the ratio of hydrolysis fortriolein:tripalmitolein:trilinolein of 100:65:82. Of the saturated fattyacid triglycerides, only tripalmitin showed any reactivity withUNLipase. The ratio of hydrolysis of triolein to tripalmitin wasapproximately 33:1.

2. Hydrolysis of Common Acyl Triglycerides with UNLipase

Twenty grams of hard-bodied tallow, lard, palm kernel oil or peanut oilwere treated with 5% (v/v) of cell free fermentation broth of mutant 9-2which contained UNLipase. The reaction was run at 30 degrees C. for 22hours, with mechanical agitation at about 200 rpm. Hard-bodied tallowwas hydrolyzed, resulting in free fatty acids that were composed of 87%oleic acid and 13% other unsaturated fatty acids. Lard was hydrolyzed byUNLipase yielding free fatty acids which were 99% unsaturated. Palmkernel oil, which contains approximately 17% by weight unsaturated fattyacids in the triglycerides, was hydrolyzed by UNLipase to yield freefatty acids which were 97% unsaturated. Peanut oil, which is 80% oleicand linoleic acids by weight, was hydrolyzed by UNLipase to yield freefatty acids which were 100% unsaturated.

3. Hydrolysis of Simple Esters with UNLipase

Simple esters were subjected to UNLipase to determine the scope andextent of UNLipase selectivity. The esters evaluated were methyl estersof propionic, caprylic, nonanoic, caproic, palmitic and oleic acids.Esters were prepared at about 50 mM in isooctane and subjected toUNLipase at 37 degrees C. for 4 hours. Only the methyl ester of oleicacid demonstrated any appreciable hydrolysis as catalyzed by UNLipase.The methyl esters of propionic, caprylic, caproic and nonanoic acidswere not hydrolyzed by UNLipase. Approximately 2% of the methylpalmitate reacted, whereas 67% of the methyl oleate was hydrolyzed.

4. Esterification and Transesterification of UNLipase

Concentrated aqueous preparations of lipase were used to test the estersynthesis properties of UNLipase. These preparations contained 50-200 mgof fatty acid, 0.5 ml concentrated broth, 0.5 ml water (buffer) and100-300 ul of alcohol. Reactions were run at either 27, 30 or 37 degreesCelsius for 16 to 24 hours. The reaction was stopped by adding 2.0 mlether.

Fatty acid and ester were extracted into ether and evaluated by thinlayer chromatography. The esterification of oleic acid with variousalcohols is present in Table 1. The results indicate that oleic esterswere synthesized with 1° and 2° alcohols, even cyclic alcohols, but theone tertiary alcohol tested did not react with oleic acid in thepresence of lipase.

                  TABLE 1                                                         ______________________________________                                        Alcohol Selectivity of Oleic Acid Esterification                              Alcohol             Ester Formed                                              ______________________________________                                        Methanol            + + + +                                                   Ethanol             + + + +                                                   n-butanol           + +                                                       2-octanol           + + + +                                                   3-pentanol          + + + +                                                   Glycerine           + + +                                                     Cyclohexanol        + +                                                       t-butanol            --                                                       ______________________________________                                    

The fatty acid selectivity of the lipase in esterification reactions wasalso evaluated in the manner described above, with results analyzed bythin layer chromatography, GC, HPLC and IR. The results are presentedbelow in Table 2.

                  TABLE 2                                                         ______________________________________                                        Fatty Acid Selectivity of Lipase Esterification                               Fatty Acid     Geometry     Ester Formation                                   ______________________________________                                        Oleic          cis, 9, 10   + + + +                                           Elaidic        trans, 9, 10  --                                               Petroselenic   cis, 6, 7     --                                               Vaccenic       cis, 11, 12   --                                               Undecenoic acid                                                                              10, 11        --                                               Palmitoleic    cis, 9, 10   + + + +                                           Linoleic       cis, 9, 10; 12, 13                                                                         + + + +                                           Linolenic      cis, 9, 10; 12, 13;                                                                        + + + +                                                          15, 16                                                         Gamma Linolenic                                                                              cis, 6, 7; 9, 10;                                                                           --                                                              12, 13                                                         Oleic + Undecenoic acid     ++                                                ______________________________________                                    

The conclusions which can be drawn from these data are the lipase has ahighly defined selectivity not only for the position of the double bondbut the geometry. The selectivity appears to be strictly a cis 9, 10double bond in monounsaturated fatty acids. For polyunsaturates, the cis9, 10 bond is also required, however, the lack of reactivity of gammalinolenic indicates that in addition to the cis 9, 10 double bond, adouble bond between the carbonyl carbon and the 9,10 double bond is nottolerated. A double bond removed by only one carbon, 10-undecenoic acid,disrupts the chemistry of the active site.

In fact, 10-undecenoic acid acts as an inhibitor of the esterificationof oleic acid, this suggests that the interaction between the enzyme andthe double bond is occurring, causing the inhibition.

Collectively, the reactivities outlined above suggest a model of theactive site. Reactivity (esterification) requires an interaction betweena double bond and some site on the enzyme. One possible explanation isthat this interaction anchors the fatty acid substrate in place andpositions the reactive carbonyl carbon at the catalytic site of theenzyme.

The esterification of fatty acid mixtures was evaluated using typicalfatty acid mixtures derived from pressure-split beef tallow, henceforthreferred to as PFA. Samples of PFA were spiked with pentadecanoic acidas an internal standard. The resulting products were analyses by eitherHPLC (reverse phase C-18 column) or GC (FFAP capillary column). Onlyesters of oleic, palmitoleic and linoleic acids were detected. Linolenicacid concentration in the PFA was deemed too low to be able to determineester formation. Stearic, palmitic, myristic and pentadecanoic acid(internal standard) were not esterified. Thus, complex mixtures of fattyacids can be treated with the selective lipase to yield only esters offatty acids containing the cis 9, 10 double bond.

5. Purification of UNLipase

UNLipase was purified from fermentation broth after removal of the cellmass by centrifugation by applying the following series of steps:

A. Biocryl BPA-1000 cation exchange chromatography to clarify thecell-free broth of nonproteinaceous material;

B. Concentration of the UNLipase by ethanol precipitation followed bycentrifugation;

C. Resuspension of the ethanol precipitation, followed by hydrophobicinteraction chromatography on octyl-sepharose;

D. Chromatography on Q-Sepharose with final concentration of the lipaseby ultrafiltration using Centricon 30 ultrafiltration units.

A single protein band was confirmed by electrophoresis. Analyticalisoelectric focusing indicated two major and two minor isozymes in theph range of 4.0-4.6. Chromatofocusing isolated the major isozyme(pI=4.5) which demonstrated the highest degree of selectivity for oleicacid. The enzyme (UNLipase) had a molecular weight of approximately65,000 kDa with sites of glycosylation which were sensitive toendoglycosidase H.

In order to illustrate the practice of this invention, the followingexamples are included.

EXAMPLE 1

Strain NRRL Y-552 was grown on nutrient agar for 3 to 4 days.Single-cell arthrospores were then rinsed from the surface of the plateswith sterile distilled water. The cells were then used to determine thetime of exposure to UV light that was required for a 90% kill(indicating highly successful mutagenesis). This was done in thebiosafety hood (Nuaire) which is equipped with a UV light. Five mls ofthe arthrospore suspension were placed in sterile petri dishes thenexposed to the UV light for various periods of time. It was determinedthat 90 seconds of exposure resulted in better than 90% kill rates. Themutants thus produced were added to 50 mls of bacto-peptone broth (5%)and placed on a shaker at 8° C. for 24 hours. (This was given as arecovery time for the survivors.) The UV irradiated suspensions werethen placed in sterile 50 ml test tubes and frozen at -5° C. Of the fewUV irradiated survivors more than 99.9% were killed by exposure to thefreezing treatment. (The hypothesis for survival was that the membraneshighest in unsaturated fatty acids would provide an advantage tosurvival of the freezing conditions.) These few survivors were thenscreened for lipase production and fatty acid specificity in thestandard lipase assay using triolein or tripalmitin as the substrate(assay described above). One mutant, 9-2, resulted which had better thana 25:1 selectivity for oleic acid versus palmitic acid (in this assay)when pure triglycerides of each were tested. This enzyme was designated"UNLipase" for its selection of unsaturated fatty acids.

Although the initial work with 9-2 resulted in growing the organism in amodified standard broth (Tsujisaka et al. 1973), work was undertaken toimprove the production of the UNLipase enzyme. It was determined earlyin our work that having fat or oil in the medium induced other lipasesproduced by Geotrichum strains. Thus fat or oil was eliminated from themedium. Then improvements for Bacto-Peptone were sought. A series ofpeptones or other organic nitrogen sources were tested including soypeptone, trypticase® (BBL) peptone, casamino acids, NZ amine® (SheffieldProducts) and casein. It was determined that trypticase® peptone at 5%resulted in the highest levels of UNLipase production.

The next important discovery was that the addition of a sugar or sugaralcohol either had no effect on UNLipase production (e.g. mannitol andmaltose) or actually inhibited UNLipase production (e.g. fructose,glucose, and sucrose). Next, the salt constituents were examined in thestandard medium. Additions of both MgSO₄ at 0.05% (w/v) and KH₂ PO₄ at0.1% (w/v) were shown to benefit the production of the enzyme. Theinclusion of these two salts in the medium gave a doubling of measuredhydrolytic activity when assayed using the standard assay. Increasingthe concentration of MgSO₄ to 0.5% gave no further enhancement. It wasfound that calcium additions (0.1 to 0.5%) to the medium did not enhancethe lipase production. Thus the UNLipase enzyme can be producedroutinely in a medium containing 5% trypticase peptone, 0.1% MgSO₄, 0.5%KH2PO₄ with no pH adjustment. Fifty mls of this medium are placed in 500ml baffled flasks (Bellco) then shaken at 250 rpms at 25°-30° C.

The UNLipase enzyme was produced and optimized in mutant 9-2. The nextgoal was to find a mutant with enhanced productivity. Thus themutagenesis of mutant 9-2 was undertaken as described above but theselection protocol was altered. In this case, after the 8° C. recoveryperiod the mutant suspensions were placed in 50 ml sterile test tubesand frozen at -55° C. The period of freezing was then interrupted bythawing periods (about 4 hours) and followed by freezing at -55° C.Mutants were screened for lipase activity and selectivity. One mutant,9-2-3-9, survived a cycle of 3 weeks of freezing which had beeninterrupted by 3 thaw cycles. The mutant 9-2-3-9 was distinctlydifferent from its parent (9-2) in its colony morphology when grown onnutrient agar. The colony type was much more aerial than 9-2. The mostdistinctive feature was that this mutant, although it produced less cellmass when grown in culture than 9-2, actually expressed much more enzymeactivity.

EXAMPLE 2

The mutant 9-2 was grown in the medium described above. Fifty mls wereadded to 500 ml baffled flasks (Bellco) and placed on a shakermaintained at 30° C. and shaken at 250 rpms. Production reaches a peakat about 30 hours, then declines slightly and remains low. The enzymewas harvested at 30 hours for a series of hydrolytic tests. Thecollection of the enzyme involves centrifugation of the broth at 5000rpms in the Beckman GSA rotor for 10 minutes. The cell free broth wasthen decanted from the cell pellet. In some cases, high activitysuspension were produced by a 70% ammonium sulfate precipitation of thebroth.

EXAMPLE 3

To demonstrate the practical aspects of UNLIpase selective fatsplitting, ten pounds of edible lard was placed in a 15 liter reactionvessel with temperature control at 30 degrees C and agitation rates ofbetween 300-500 rpm. Cell-free fermentation broth from culture of mutant9-2 or twice-concentrated cell-free broth was added to initiate thehydrolysis. The broth provided the necessary water of reaction.Hydrolysis progress was monitored periodically by determining the acidvalue (AOCS Method Te 1a-64) of an aliquot of the reaction mixture. Thecomposition of free fatty acids at the end of the reaction was 99%unsaturated fatty acids. The ratio of oleicpalmitoleiclinoleic was78:3:18.

What is claimed is:
 1. A biologically pure culture of a strain ofGeotrichum candidum having all the identifying characteristics of thestrain ATCC
 74170. 2. The biologically pure culture of claim 1 whereinsaid strain is Geotrichum candidum ATCC 74170.